1. Field of the Invention
The present invention relates to laser scattering defect inspection systems and methods for detecting small defects present on the surface of a workpiece using light scattering.
2. Description of the Related Art
In the related art, laser scattering defect inspection systems are known as systems for detecting small defects present on the surface of workpieces such as semiconductor wafers, patterned wafers, or mask blanks. The laser scattering defect inspection systems are configured to irradiate a laser beam on a wafer as the workpiece and detect light scattered from the surface, thereby detecting the presence of defects.
A spiral scanning defect inspection system, which is a typical defect inspection system, irradiates a laser beam on a wafer from a fixed position while rotating and transporting the wafer in a radial direction thereof, thereby scanning (spirally scanning) an entire surface of the wafer in a spiral form. Moreover, as effective methods of scanning a wafer surface, methods disclosed in U.S. Pat. Nos. 5,712,701, 6,118,525, 6,292,259, and PCT/US2005/045931 are known. This method employs a complex scanning method that scans (cross-scans) a beam irradiation position from the laser side, in addition to the spiral scan. Since this scanning method minutely vibrates the beam irradiation position using an optical deflector, the beam spot size can be increased substantially, and thus, the wafer surface can be scanned effectively with fewer revolutions per minute.
However, since the scanning methods disclosed in U.S. Pat. Nos. 5,712,701, 6,118,525, 6,292,259, and PCT/US2005/045931 are complicated, there is a problem that the positional precision of the detected defect coordinates is poor. For example, during the LSI process, it is common practice to examine the presence or the location of defects using an optical defect inspection system with high throughput and, based on the thus obtained information, to investigate and classify (actual condition investigation) the defects using a review SEM (scanning electron microscope). However, if the positional precision of the detected defect coordinates is poor, it may take a considerable amount of time to locate the defects, thus deteriorating the processing efficiency.
On the other hand, the defect inspection system is also used for the final shipment inspection which is performed at the stage of wafer shipment. The final shipment inspection is performed for all wafers, and the inspected wafers are generally packaged into a case for shipment without any further processing. In this case, the number of defects becomes important, and the positional precision of the defect coordinates is not taken into consideration. Since the final shipment inspection is a total inspection, it is important to reduce the inspection time per wafer.